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Copyright © 2012 Pearson Education Inc.
PowerPoint® Lectures for
University Physics, Thirteenth Edition
– Hugh D. Young and Roger A. Freedman
Lectures by Wayne Anderson
Chapter 43
Nuclear Physics
Copyright © 2012 Pearson Education Inc.
Goals for Chapter 43
• To understand some key properties of nuclei
• To see how nuclear binding energy depends on the
number of protons and neutrons
• To investigate radioactive decay
• To learn about hazards and medical uses of radiation
• To analyze nuclear reactions
• To investigate nuclear fission
• To understand the nuclear reactions in our sun
Copyright © 2012 Pearson Education Inc.
Introduction
• How can we date ancient biological artifacts?
• Most of the mass of an atom is found in its tiny nucleus.
• Some nuclei are stable, but others spontaneously decay.
• Fission and fusion are important nuclear reactions. We would not exist without the fusion in our sun.
Copyright © 2012 Pearson Education Inc.
Properties of nuclei
• The nucleon number A is the total number of
protons and neutrons in the nucleus.
• The radius of most nuclei is given by R = R0A1/3.
• All nuclei have approximately the same density.
• Follow Example 43.1.
Copyright © 2012 Pearson Education Inc.
A nucleus of neon-20 has 10 protons and 10 neutrons.
A nucleus of terbium-160 has 65 protons and 95 neutrons.
Compared to the radius of a neon-20 nucleus, the radius of a
terbium-160 nucleus is
Q43.1
A. 9.5 times larger.
B. 8 times larger.
C. 6.5 times larger.
D. 4 times larger.
E. 2 times larger.
Copyright © 2012 Pearson Education Inc.
A nucleus of neon-20 has 10 protons and 10 neutrons.
A nucleus of terbium-160 has 65 protons and 95 neutrons.
Compared to the radius of a neon-20 nucleus, the radius of a
terbium-160 nucleus is
A43.1
A. 9.5 times larger.
B. 8 times larger.
C. 6.5 times larger.
D. 4 times larger.
E. 2 times larger.
Copyright © 2012 Pearson Education Inc.
Nuclides and isotopes
• The atomic number Z is the number of protons in the
nucleus. The neutron number N is the number of neutrons
in the nucleus. Therefore A = Z + N.
• A nuclide is a single nuclear species having specific values
for both Z and N.
• The isotopes of an element have different numbers of
neutrons.
• Follow the text discussion of nuclear spin and magnetic
moments.
• Follow Example 43.2 on proton spin flips.
Copyright © 2012 Pearson Education Inc.
NMR and MRI
• Follow the text discussion of nuclear magnetic resonance and MRI, using Figure 43.1 below.
Copyright © 2012 Pearson Education Inc.
Nuclear binding energy
• The binding energy EB of a
nucleus is the energy that
must be added to separate
the nucleons.
• Follow the text discussion of nuclear binding energy, using Figure 43.2 (right).
• Read Problem-Solving Strategy 43.1.
• Follow Example 43.3 on strongly bound nuclei.
Copyright © 2012 Pearson Education Inc.
The nuclear force
• The nuclear force binds protons and neutrons together. It is an
example of the strong interaction.
• Important characteristics of the nuclear force:
It does not depend on charge. Protons and neutrons are
bound. It has a short range, of the order of nuclear
dimensions.
Because of its short range, a nucleon only interacts with those
in its immediate vicinity.
It favors binding of pairs of protons or neutrons with opposite
spins and with pairs of pairs (a pair of protons and a pair of
neutrons, each pair having opposite spins).
Copyright © 2012 Pearson Education Inc.
Why do stable nuclei with many nucleons (those with a large
value of A) have more neutrons than protons?
Q43.2
A. An individual nucleon interacts via the nuclear force
with only a few of its neighboring nucleons.
B. The electric force between protons acts over long
distances.
C. The nuclear force favors pairing of both neutrons and
protons.
D. both A. and B.
E. all of A., B., and C.
Copyright © 2012 Pearson Education Inc.
Why do stable nuclei with many nucleons (those with a large
value of A) have more neutrons than protons?
A43.2
A. An individual nucleon interacts via the nuclear force
with only a few of its neighboring nucleons.
B. The electric force between protons acts over long
distances.
C. The nuclear force favors pairing of both neutrons and
protons.
D. both A. and B.
E. all of A., B., and C.
Copyright © 2012 Pearson Education Inc.
Nuclear models
• Follow text discussion
of the liquid-drop
model and the shell
model.
• Figure 43.3 (right)
shows the approximate
potential-energy
functions for a nucleon
in a nucleus.
• Follow Example 43.4.
Copyright © 2012 Pearson Education Inc.
Nuclear stability and radioactivity
• Radioactivity is the decay of
unstable nuclides by the
emission of particles and
electromagnetic radiation.
• Figure 43.4 (right) is a Segrè
chart showing N versus Z for
stable nuclides.
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Alpha decay
• An alpha particle is a 4He nucleus.
• Figure 43.5 shows the alpha decay of the 226Ra nuclide.
• Follow Example 43.5.
Copyright © 2012 Pearson Education Inc.
Which kinds of unstable nuclei typically decay by emitting an
alpha particle?
Q43.3
A. those with too many neutrons
B. those with too many protons
C. those with too many neutrons and too many protons
D. Misleading question—the numbers of neutrons and
protons in a nucleus are unrelated to whether or not it
emits an alpha particle.
Copyright © 2012 Pearson Education Inc.
Which kinds of unstable nuclei typically decay by emitting an
alpha particle?
A43.3
A. those with too many neutrons
B. those with too many protons
C. those with too many neutrons and too many protons
D. Misleading question—the numbers of neutrons and
protons in a nucleus are unrelated to whether or not it
emits an alpha particle.
Copyright © 2012 Pearson Education Inc.
Beta and gamma decay
• There are three types of beta decay: beta-minus, beta-plus, and electron capture.
• A beta-minus – particle is an electron.
• A gamma ray is a photon.
• Follow the text discussion of beta decay and gamma decay.
• Follow Example 43.6 on cobalt-60.
• Follow Example 43.7 on cobalt-57.
Copyright © 2012 Pearson Education Inc.
Which kinds of unstable nuclei typically decay by emitting an
electron?
Q43.4
A. those with too many neutrons
B. those with too many protons
C. those with too many neutrons and too many protons
D. Misleading question—the numbers of neutrons and
protons in a nucleus are unrelated to whether or not it
emits an electron.
Copyright © 2012 Pearson Education Inc.
Which kinds of unstable nuclei typically decay by emitting an
electron?
A43.4
A. those with too many neutrons
B. those with too many protons
C. those with too many neutrons and too many protons
D. Misleading question—the numbers of neutrons and
protons in a nucleus are unrelated to whether or not it
emits an electron.
Copyright © 2012 Pearson Education Inc.
Which kinds of unstable nuclei typically decay by emitting a
gamma-ray photon?
Q43.5
A. those with too many neutrons
B. those with too many protons
C. those with too many neutrons and too many protons
D. Misleading question—the numbers of neutrons and
protons in a nucleus are unrelated to whether or not it
emits gamma rays.
Copyright © 2012 Pearson Education Inc.
Which kinds of unstable nuclei typically decay by emitting a
gamma-ray photon?
A43.5
A. those with too many neutrons
B. those with too many protons
C. those with too many neutrons and too many protons
D. Misleading question—the numbers of neutrons and
protons in a nucleus are unrelated to whether or not it
emits gamma rays.
Copyright © 2012 Pearson Education Inc.
Natural radioactivity
• Figure 43.7 (right) shows a Segrè chart for the 238U decay series.
Copyright © 2012 Pearson Education Inc.
Activities and half-lives
• The half-life is the time for the number of radioactive nuclei to decrease to one-half of their original number.
• The number of remaining nuclei decreases exponentially (see Figure 43.8 at right).
• Follow the text discussion of decay rates and radioactive dating.
• Follow Example 43.8 on 57Co activity.
• Follow Example 43.9 on radio-carbon dating.
Copyright © 2012 Pearson Education Inc.
As a sample of radioactive material decays, the decay rate
Q43.6
A. is directly proportional to the half-life and directly
proportional to the number of radioactive nuclei remaining.
B. is directly proportional to the half-life and inversely
proportional to the number of radioactive nuclei remaining.
C. is inversely proportional to the half-life and directly
proportional to the number of radioactive nuclei remaining.
D. is inversely proportional to the half-life and inversely
proportional to the number of radioactive nuclei remaining.
Copyright © 2012 Pearson Education Inc.
As a sample of radioactive material decays, the decay rate
A43.6
A. is directly proportional to the half-life and directly
proportional to the number of radioactive nuclei remaining.
B. is directly proportional to the half-life and inversely
proportional to the number of radioactive nuclei remaining.
C. is inversely proportional to the half-life and directly
proportional to the number of radioactive nuclei remaining.
D. is inversely proportional to the half-life and inversely
proportional to the number of radioactive nuclei remaining.
Copyright © 2012 Pearson Education Inc.
Biological effects of radiation
• Follow the text discussion of the biological effects of radiation.
• Table 43.3 gives the RBE for several types of radiation.
• Figure 43.9 shows sources of U.S. radiation exposure.
• Follow Example 43.10 about a medical x ray.
Copyright © 2012 Pearson Education Inc.
Nuclear reactions
• A nuclear reaction is a rearrangement of nuclear components due to bombardment by a particle rather than a spontaneous natural process.
• The difference in masses before and after the reaction corresponds to the reaction energy Q.
• Follow Example 43.11, which looks at exoergic and endoergic reactions.
Copyright © 2012 Pearson Education Inc.
Nuclear fission
• Nuclear fission is a decay process in which an unstable nucleus splits into two fragments (the fission fragments) of comparable mass.
• Figure 43.11 (right) shows the mass distribution of the fission fragments from the fission of 236U*.
Copyright © 2012 Pearson Education Inc.
Liquid-drop model
• The liquid-drop model helps explain fission. See Figure 43.12 below.
• Figure 43.13 (right) shows the potential energy function of two fission fragments.
Copyright © 2012 Pearson Education Inc.
Chain reactions
• The neutrons released by fission can cause a chain reaction (see Figure 43.14 below).
Copyright © 2012 Pearson Education Inc.
Nuclear reactors
• A nuclear reactor is a system in which a controlled nuclear chain reaction is used to liberate energy.
• Figure 43.15 below illustrates a nuclear power plant.
• Follow Example 43.12.
Copyright © 2012 Pearson Education Inc.
Nuclear fusion
• In a nuclear fusion reaction, two or more light nuclei fuse to form a larger nucleus.
• Figure 43.16 below illustrates the proton-proton chain, which is the main energy source in our sun.
• Follow Example 43.13.
Copyright © 2012 Pearson Education Inc.
Why does nuclear fusion of hydrogen require high temperatures?
Q43.7
A. Positive charges repel each other.
B. The nuclear force only acts at short range.
C. both A. and B.
D. neither A. nor B.
Copyright © 2012 Pearson Education Inc.
Why does nuclear fusion of hydrogen require high temperatures?
A43.7
A. Positive charges repel each other.
B. The nuclear force only acts at short range.
C. both A. and B.
D. neither A. nor B.